The semiconductor industry is constantly producing smaller and more complex semiconductors, sometimes called integrated circuits (ICs) or chips. This trend has brought about the need for smaller semiconductor packages with smaller footprints, higher lead counts, and better electrical and thermal performance, while at the same time meeting accepted reliability standards.
As memory demands increase, so does the need for increased memory capacity. A problem with adding more ICs to a circuit board for increased memory capacity, is that placement of the ICs on the circuit board is spread out, which often requires reconfiguration of the circuit board connectors and their associated connections on a motherboard. This ultimately leads to replacing the circuit board and in some cases the entire motherboard.
One solution to adding more memory capacity without spreading out ICs on a circuit board is by using a 3-dimensional chip stacking technique to form multi-chip modules (MCMs), otherwise known as stacked semiconductor modules, or stacked IC modules. These MCMs have a high memory capacity, while retaining a relatively small size. Examples of these techniques are disclosed in U.S. Pat. Nos. 5,104,820, and 5,279,991, and U.S. patent application Ser. Nos. 09/471,304 and 09/685,941, all of which are incorporated herein by reference.
These prior art stacked semiconductor modules require all IC dice within the MCM to be in adequate working order after assembly. If any of the IC dice are found to be defective during or after the assembly process, the entire MCM is scrapped, as there is no means of utilizing only the working IC dice.
The manufacturing process of these MCMs is typically as follows. Each manufactured IC die is tested for desired characteristics, such as speed BIN, operating frequency, etc. The IC dice are then sorted based on their measured characteristics. For example, all 600 MHz dice are collected together, all 700 MHz dice are collected together, and all 800 MHz dice are collected together. The IC dice from a single sorted group are then assembled into stacks and packaged together to form a stacked semiconductor module or MCM. For example, multiple 800 MHz IC dice are packaged together to form an In-line memory module, such as a RAMBUS PC800 RDRAM™ RIMM™ (a RDRAM™ is a RAMBUS Dynamic Random Access Memory, and a RIMM™ is a RAMBUS In-line Memory Module).
The problem with the above process for forming MCMs, is that if during or after assembly it is found that one of the IC dice is not operating or does not have the required characteristics, for instance because an IC die was damaged during assembly, that MCM is scrapped. The cost of scrapping modules can be significant. Furthermore, if only one IC die is found to be unacceptable, the whole MCM is scrapped, including the IC dice within the MCM that were found to be acceptable. This leads to a wastage of potentially valuable IC dice. Moreover, the cost of scrapping MCMs prohibits the manufacture of MCMs having many stacks of IC dice, because if one IC die in a single stack is found to be unacceptable, the whole MCM is scrapped, wasting even more IC dice.
In view of the foregoing it would be highly desirable to provide an MCM that overcomes the shortcomings of prior art devices by addressing the problem of having to scrap entire MCMs when one or more of the embedded IC dice are found to be unacceptable.